Databases and Database Management Systems

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Databases and Database Management Systems
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What is Data? What is the difference between
Data and Information?
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• Examples of a Database
• Student Records at UCC
• Credit Card details
• Directory Enquiries
• Insurance Broker
• Library System

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What is data?

• What is data?
• Data is the raw material from which information
  is obtained
• The processing of data consists of manipulating
  it into a form which provides information in a
  format that is meaningful and usable to the
  manager or other end-user
• Arrival of computer processing meant this process
  was mimicked.
• Automation of existing systems. This is a
  traditional file-based system

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History of Information

• Initially the information needs of an
  organisation were met using a manual system.
  This system was very labour intensive.
• With the arrival of computers, the manual filing
  system was moved on to a computer. This early use
  of computers for gathering information was called
  the file based approach.

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What is a file-based system?

• A collection of application programs that
  perform services for the end-users such as the
  production of reports. Each program defines and
  manages its own data. (Connolly Begg)
• An early attempt to computerise the manual filing
  system used
• The operation of these systems closely resembles
  that of a manual system. All that is really
  achieved is the automation of the existing system.

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File Based Approach
RESPONSIBILITY HELD
APPLICATIONS
DATA HELD
PAYROLL PROGRAM
Employee Name, Age, Address, Hours, Pay Rate
Payroll Dept.
ADMIN. PROGRAM
Dept. Name, Employee Name, Emp. Address, Office
Location
Dept. Managers
PROJECT SCHEDULING PROGRAM
Project Name, Start Date, Staff Name, Staff
Address, Project Hours
Project Leaders
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What are the limitations of the file-based system?

• Separation and isolation of data
• Decentralised data makes cross-referenced
  searching slow and difficult
• Duplication of Data
• Wastes time and money for entering and storage,
  leads to corruption of data integrity
• Program-Data Dependence

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What are the limitations of the file-based system?

• Incompatibility of files
• Structure and format is dependent on the
  development language and platform of the
  application
• Fixed queries and proliferation of application
  programs
• Ad Hoc querying and reporting code to be written
  from scratch

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What is a Database?

• a shared collection of logically related data
  (and a description of this data), designed to
  meet the information needs of an organisation
  (Connolly Begg)
• Implications? Centralised (minimal duplication),
  self-describing (program independent to an
  extent), logical structure (entities, attributes
  and relationships).

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Advantages of a Database

• Data Integrity is easier to maintain as all data
  is held in on central location
• A database system allows for ad-hoc queries and
  caters to complex questions involving the
  interaction and relationships between the various
  data items in the database to be investigated
• Security
• Minimisation of data duplication
• Control of data redundancy
• Improved Maintenance

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Disadvantages of a Database

• Complexity increased functionality means the
  system is more complex and sophisticated in
  structure
• Size complexity and functionality makes the
  DBMS a large piece of software, taking up a lot
  of space
• Cost of DBMSs the cost can vary depending on
  functionality required and the environment
• Additional Hardware Costs
• Cost of Conversion - conversion of existing
  systems
• High Impact of Failure - as a result of
  centralisation

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What is a DBMS?

• The DBMS is a piece of software whose main
  function is to organise data so it can be
  retrieved, modified or updated at will. It is the
  link between the user and the data, giving access
  to the data required for the systems and their
  application programs.
• A software system that enables users to define,
  create, and maintain the database and provides
  controlled access to this database (Connolly
  Begg).

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Database Management System
APPLICATIONS
DATA HELD
PAYROLL PROGRAM
Database
ADMIN. PROGRAM
Employee Administration and project Details
DBMS
PROJECT SCHEDULING PROGRAM
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Explanation of a DBMS

• In the database structure, each system draws its
  data via the database management system, so each
  systems program interacts with the DBMS rather
  than the database files themselves (e.g MS
  Access)
• A DBMS can be described as an intelligent filing
  cabinet, as it performs all the functions of an
  efficient filing clerk

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Components of a DBMS

• Data definition language is used to define the
  database (types, structure and constraints)
• Data Manipulation Language is used to insert,
  update, delete and retrieve data. Utilises a
  flexible, ad hoc, query language
• There are two types of query language, procedural
  (one record at a time, specifies how) and
  non-procedural (sets of records, specifies
  what).
• Access control includes security, integrity,
  concurrency, recovery and catalogues.

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Components of a DBMS

• End-users use VIEWS which makes the DBMS
  transparent in its activities
• A DBMS consists of hardware (machines, network
  connections, physical storage), software (OS,
  DBMS, applications), data, procedures and people
  (administrators, designers (logical and
  physical), programmers and end-users.
• Advantages Less redundancy, improved
  consistency, information, integrity, security,
  scalability, flexibility, productivity,
  concurrency, maintenance and recovery.
• Disadvantages complexity, size, cost,
  generalisation, high impact of failure.

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Roles in Database Management System

• Database Administrator
• Database Designers
• Application Programmers
• End-Users

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Architecture

• Most DBMSs use a three-level architecture
  External, Internal and Conceptual
• Internal - describes how the data is stored in
  the database (space allocation, compression,
  encryption etc.) and interfaces with the OS to
  manage files in physical storage
• Conceptual - Describes what data is stored and
  the relationships between data
• External - Defines the users view of the data

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Reasons for Three-Tier Architecture